Overcoming soil nutrient constraints to crop production in West Africa: Importance of fertilizers and priorities in soil fertility research

The Alfisols, Oxisols, Ultisols and Inceptisols which dominate the soils of West Africa have sustained crop growth for a very long time. As a consequence, their fertility has become perilously low and the task of increasing or even maintaining the productive capacity of these soils has become perhaps the greatest challenge to agricultural scientists in this latter half of the 20th century.Water is useful not only for the growth of plants but also for the efficient use of costly inputs such as fertilizers. On the other hand, fertilizers increase the water-use efficiency. Such interactions must be closely studied so as to maximize the impact of inputs of agricultural production.The nutrients in the soil are always in a state of flux, with additions and subtractions. Monitoring the dynamics of the nutrients would promote their efficient use by crops and prolong the productive life of the soils.Several models currently exist for the study of organic matter dynamics in soils. These models should be applied to the West African situation since it is vital to develop management practices that can promote efficient use of nutrients released during mineralisation of soil organic matter.Judicious fertilizer use in West Africa should be promoted as this practice will enhance agricultural production while protecting the fragile environment.     

The role of fertilizers in sustaining agriculture in sub-Saharan Africa

African farmers have relied traditionally on fallowing for up to 15 years to restore soil fertility. Leaving land unproductive for such periods is a luxury many regions cannot afford, given the contemporary decline in per capita food production (1%/year). Thus, alternative soil fertility maintenance measures such as agroforestry, novel intercropping systems, residue conservation, the use of manure, soil amendments, and fertilizer have recently been given greater emphasis. The Food and Agriculture Organization (FAO) estimates that 75% of the increase in regional food production must come from intensive production. However, fertilizer use in sub-Saharan Africa is only one tenth of the world average. The small size of fertilizer markets in most countries is an important contributing factor in relatively high farm-gate prices and low fertilizer use. There is significant scope for improving the efficiency of fertilizer procurement and distribution in the region. Most countries can substantially reduce farm-gate prices by changing to higher analysis formulas, relaxing specifications, importing in bulk and bagging locally, and improving systems of distribution. Various options of fertilizer production are discussed in this context. Intensification in areas where environmental constraints are limited and surplus production can be marketed may alleviate the demographic pressures to cultivate marginal land where increased land and labor productivity is unlikely. Although substantial effort should be made to research sustainable farming system options for marginal lands, efforts in the more resilient environments should concentrate on increased crop production, using inputs where feasible. Provisions should be made for adequate support in the infrastructural, institutional, and policy spheres to transform these regions into granaries.     

硝态氮在经济作物专用肥的应用

烟草、棉花、辣椒等经济作物的专用肥中配入一定比例的硝态氮 ,可提高其产量、质量 ,介绍几种经济作物专用肥的原料配比及产品质量     

Studies on the substitution of inorganic fertilizers with organic manure and their effect on soil fertility in rice—wheat rotation

Field studies on the substitution of N and P fertilizers with farm yard manure (FYM) and their effect on the fertility status of a loamy sand soil in rice—wheat rotation are reported. The treatments consisted of application of 12 t FYM ha^–1 in combination with graded levels of N and P. Application of fertilizer N, FYM and their different combinations increased the rice yield significantly. There was no significant response to P application. The magnitude of response to the application of 12 t FYM and its combined use with each of 40 kg and 80 kg N ha^–1 was 0.7, 2.2 and 3.9 t ha^–1 respectively. Application of 120 kg N ha^–1 alone increased the yield by 3.9 t ha^–1, and was comparable to rice yield obtained with 80 kg N and 12 t FYM ha^–1. This indicated that 12 t FYM ha^–1 could be substituted for 40 kg N as inorganic fertilizer in rice. In addition FYM gave residual effects equivalent to 30 kg N and 13.1 kg P ha^–1 in the succeeding wheat. The effect of single or combined use of inorganic fertilizers and FYM was significantly reflected in the build up of available N, P, K and organic carbon contents of the soil. The relationship for predicting rice yield and nutrients uptake were also computed and are discussed.     

有机中微肥的生产及其应用前景

我国中低产田面积占总耕地面积70%以上,其中大部分存在有机质和中微量元素缺乏和肥料利用率低的问题。为防止中微量元素施入土壤后被固定而失效,提出利用废弃资源,生产有机中微肥(如氨基酸、木质素磺酸、腐植酸中微肥等),其生产成本比EDTA螯合中微肥低,并简要介绍了各种有机中微肥的生产工艺过程。只要做到测土施肥,有针对性加入有机中微肥,即可达到提高作物产量、品质,提高肥料利用率,提高土壤肥力的良好效果。     

Optimum phosphate and potassium levels in potato tops

The feasibility of using chemical plant analysis for early diagnosis of phosphate and potassium deficiencies in potatoes was studied. Plant tops (leaves including stems) were sampled from fertilizer field experiments and analyzed for total N, P and K. The inverse relationship between plant N concentration and plant age was used for correcting plant P and K concentration to a standard N content, thus partly eliminating growth stage differences.Maximum tuber yields were associated with leaf P above 0.5% and leaf K above 5%, both at 5% N in DM. With each percent decrease in N concentration the critical value for P decreases by about 0.1% and that for K by about 0.5%. Serious yield reductions may be found below 0.3% P and below 3% K, again at an N-level of 5%.     

Application of liquid cattle manure and inorganic fertilizers affect dry matter,nitrogen accumulation,and partitioning in maize

Efficient use of N applied in the form of organic and inorganic fertilizers is important in maize (Zea mays L.) production to maximize producer’s economic returns and maintain soil and water quality. A field study was conducted for three consecutive years (2003–2005) in Thessaloniki, Greece to investigate whether liquid cattle manure can be used to replace inorganic fertilizers and also whether inorganic fertilizer can be applied preplant or as a combination of preplant and sidedress and can affect maize growth, development and N use efficiency. The treatments were control (unfertilized), liquid dairy cattle manure (Manure), application of 260 kg N ha⁻¹ year⁻¹ as basal dressing (N-single), application of 130 kg ha⁻¹ year⁻¹ N as basal dressing before sowing and 130 kg N ha⁻¹ when plants were at the eight-leaf stage (V8) (N-split). In 2 out of the 3 years of the study there was a significant positive effect of fertilizer application on maize growth, development, N uptake, and partitioning compared with the control. Dry matter production was increased by an average of 39% during the 2 years in plots fertilized either with manure or inorganic fertilizers than the control plots. Also from the yield components kernel weight per ear and number of kernels per ear were increased by an average of 35% and 32%, respectively in the fertilized plots compared with the control plots. Chlorophyll level was affected as it was increased by an average of 18%, 14%, and 18% at the ten-leaf stage (V10), silking and milk stage, respectively in the fertilization treatments compared with the control. Similar trend was observed in the other parameters that were studied. No differences were found between the manure and the different times of N application which indicates that manure can be used to replace inorganic fertilizer. Applying N either preplant in a single application or in split application (half of N preplant and half as sidedress) did not have any effect on any characteristics that were studied indicating that preplant application can be used as it is more cost effective. The present study indicates that liquid cattle manure can be used to replace inorganic fertilizers and also that there was no difference between preplant and sidedress application of N.     

The role of soil pH in the dissolution of phosphate rock fertilizers

The influence of soil pH on the dissolution of phosphate rock fertilizers was investigated in laboratory experiments with reactive North Carolina phosphate rock (PR) in a lateritic soil adjusted to several pH values. Increased soil pH resulted in decreased dissolution as estimated by the increase in exchangeable calcium (Ca) method. The extent of PR dissolution was related to soil pH by an equation of the form Log Ca = a–b pH, and it increased with contact period and rate of PR application. Increased plant available P, as estimated by NaHCO₃ soluble-P (BicP) was about one third of the P dissolved from PR. BicP was related to soil pH by an equation of the form Log Bic P = c–d pH. Dissolution of PR in soil can be considered as a simple chemical reaction between apatite and hydrogen ions supplied by soil constituents.     

生物菌剂与腐植酸肥配施对模拟复垦土壤的微生物数量和作物养分含量影响的研究

采在温室条件下,采用盆栽试验方法研究了生物菌剂与腐植酸肥配施的肥效及其对土壤微生物群落分布的影响。试验共设生物菌剂与腐植酸肥配施、腐植酸肥、化肥和无肥（CK）、生物菌剂5个处理。结果表明,施用生物菌剂与腐植酸肥配施能显著提高土壤微生物数量,土壤中的细菌、真菌和放线菌总数均有显著增加;同时,能显著提高作物养分含量及生物量。     

Effect of organic and inorganic phosphate fertilizers and their combination on maize yield and phosphorus availability in a Yellow Earth in Myanmar

Phosphorus (P) deficiency is a major constraint for crop production in many parts of the world including Myanmar and field research into management of P fertilizers and P responsiveness of crops on infertile soils has been limited. The purpose of this study is to determine maize yield response to different forms of P fertilizers on an acidic (pH 4.9) P deficient (Olsen-P 8 mg kg⁻¹) Yellow Earth (Acrisol) in Southern Shan State, Myanmar and to establish relationships between soil Olsen-P test values (0.5 M sodium bicarbonate extracted P) and maize yield. Field experiments were conducted during two cropping seasons. There were 15 treatments in total: P was applied at seven rates of a soluble P fertilizer as Triple superphosphate (TSP) (0–120 kg P ha⁻¹) to establish a P response curve; one rate of a partially soluble P fertilizer (Chinese partially acidulated phosphate rock, CPAPR) and two organic P fertilizers (farmyard manure (FYM) and Tithonia diversifolia) at 20 kg P ha⁻¹; combination of TSP and CPAPR at 20 kg P ha⁻¹ with FYM and Tithonia at 20 kg P ha⁻¹; an additional treatment (TSP 20 kg P ha⁻¹ plus 2.5 t ha⁻¹ dolomite) for assessing the liming effect of a local dolomite. In Year 1, applications of TSP at 40–60 kg P ha⁻¹ produced near maximum grain yields, whereas in Year 2 this could be achieved with a reapplication of 20–30 kg P ha⁻¹ on top of the residual value of the Year 1 application. In both years, CPAPR, TSP and Tithonia at 20 kg P ha⁻¹ significantly increased maize grain yield, but FYM failed to increase grain yield. In Year 1, CPAPR and TSP effects on grain yield were higher than that of Tithonia but in Year 2 the effects were same for all these three treatments. In both years the combination of FYM (20 kg P ha⁻¹) with TSP (20 kg P ha⁻¹) produced significantly higher grain yield than TSP at 20 kg P ha⁻¹ whereas 40 kg P ha⁻¹ of TSP application did not significantly increase grain yield over the TSP application at 20 kg P ha⁻¹. Similar results were obtained when half the P applied as CPAPR was substituted with P from Tithonia and FMP during the first year. The combined data from the two years experiment suggests that 90% of maximum maize grain yields can be obtained by raising the Olsen-P to 30–35 mg P ha⁻¹ soil at the silking stage of growth. Olsen-P for the treatments at silking in Year 1 was: Control < FYM, Tithonia < TSP, CPAPR and in Year 2 was: Control < FYM < Tithonia < TSP, CPAPR. The results showed that for a long-term approach, repeated annual applications of Tithonia can be considered as a potential P source for improving soil P status in P deficient Yellow Earths.     

新型生物有机肥对小白菜生长和土壤肥力的影响

为了调理菜田土壤,提高小白菜的生产效益,用高温快速发酵的生物有机肥在小白菜上进行盆栽试验和生产试验。结果表明:生物有机肥能促进小白菜根长、株高、叶长、叶宽的生长,极显著提高小白菜根质量、茎叶质量、根冠比和产量;同时补充和活化土壤营养,改善土壤理化性状,促进了小白菜对各种主要养分的吸收。     

Farmer's view on soil organic matter depletion and its management in Bangladesh

Bangladesh is an agricultural country. About 80% of the total population live in rural areas. The contribution of agriculture to the gross domestic product is 30%. Rice is the major food crop while jute, sugarcane and tea are the main cash crops. Other important crops are wheat, tobacco, pulses, vegetables and fruits. Overall productivity in Bangladesh is stagnating or declining. The implication of yield stagnation or declining productivity is severe, since these trends have occurred despite rapid growth in the use of chemical fertilisers. Depletion of soil organic matter is the main cause of low productivity, which is considered one of the most serious threats to the sustainability of agriculture in Bangladesh. In Bangladesh, most soils have less than 17 g/kg and some soils have less than 10 g/kg organic matter. Farmers realise that there is a problem with soil fertility related to organic matter depletion. Farmers say that organic matter increases yield, reduces the production cost, improves crop growth and the economy, increases water-holding capacity and improves the soil structure. They recognise soil with higher organic matter content by darker brownish to black in colour. Some farmers are using fast-growing trees such as Flemingia macrophyla, Ipilipil (Leucaen leucophala), Glyricidia sepium, Boga Medula (Tephrosia candida), Dhol Kolmi (Ipomoea fistulosa), etc., as living fences, which can be used as fuel, fertiliser and fodder. To increase the soil organic matter, farmers use green manure crops, compost, quick compost, cow dung, azolla, etc. However, fuel for cooking purposes is limited and cow dung and crop residues are largely used as fuel. Crop residues are also used as fodder for livestock. Farmers expressed the wish to learn more about organic fertilizer management. However, sufficient food should be produced to keep pace with population growth. To alleviate the hunger and poverty is to increase the intensity of agricultural production and maintain favorable ecological conditions. Therefore, more organic matter should be used in the farmers' fields to sustain the soil fertility in an intensive farming system. This revised version was published online in June 2006 with corrections to the Cover Date.     

Fertilizer requirements for specified yield targets. I. Theoretical derivation of mathematical models for the computation of soil and fertilizer nutrient efficiencies

The conventional deduction procedure of computation of soil () and fertilizer () nutrient efficiencies for the amount of fertilizer required for specified yield targets does not make provision of the amount of soil nutrient derived by crops from the available pool of soil nutrients not accounted for in the amount extracted by a soil test procedure. The derivation of two mathematical models, viz., Tamil Nadu Agricultural University Model I [TNAU Model I] and Model II [TNAU Model II] is reported in this paper which aim at computing the soil () and fertilizer () nutrient efficiencies not accounted for by the conventional method.In the case of TNAU Model I, the relationship between the nutrient uptake (U) and the soil (S) and the fertilizer (F) nutrients was established by assuming a functional relationship of the type U =S +F such that 0 1 and 0 1. In TNAU Model II the same relationship was established as U =S +F + such that 0 1, 0 1 and > 0. The term in the latter model is a measure of the amount of soil nutrient the crop absorbs from a slowly available pool of nutrients not accounted for in the amounts extracted by the soil test procedure employed or applied through fertilizer.The field verification of these models is reported elsewhere.     

Plant response to the management of fluid and solid N fertilizers applied to furrow-irrigated corn

The use of fluid fertilizers has increased in recent years. Plant response to field management practices of fluid and solid N fertilizers in furrow-irrigated field studies has not been well-documented. This research studied the response of corn (Zea mays L.) to several field management practices of fluid and solid N fertilizers applied at several rates. Corn grown with sidedressed applications of the fluid fertilizers, urea ammonium nitrate (UAN) and 18-0-0+7Ca, generally had higher grain yields, higher yield efficiencies, higher ear populations, larger seed size, more kernels per ear, and a higher ear leaf N concentration than corn grown with preplant broadcast treatments of urea, ammonium nitrate (AN), and UAN. In 1988, corn grown with 280 kg N ha^–1 of AN applied preplant broadcast had a lower grain yield, yield efficiency, kernels per ear, and ear leaf N concentration, while ear population and kernel size were unchanged, in comparison to split applications of UAN at 224 kg N ha^–1. In 1989, corn grown with three split applications of UAN at 280 kg N ha^–1 had a higher grain yield and produced more kernels per ear without affecting yield efficiency, ear population, kernel size, or ear leaf N concentration compared with treatments at the 224 kg N ha^–1 rate. Use of split, side-dressed N management practices in furrow-irrigated corn should eliminate the need to use excessive N rates while maintaining grain yields and other plant responses, resulting in more efficient N use than traditionally achieved.     

Fertilizer regime and changes in the phosphate and potash status of a silty marine clay soil during 25 years

Changes in the soil phosphorus and potassium status on three farming systems in the Northeast Polder during 25 years are related to the fertilizer regime over this period.The changes in the nutrient status of the soil are reflected in fertilizer policy. High rates of phosphate dressings markedly increased the phosphate status of the soil and built up a reserve of phosphate. In contrast, the potassium status decreased by about half, because only potatoes in the rotation were dressed with potassium.Methods of fertilization are discussed and suggestions are made with regard to possible improvements.The results of this investigation have also been reported in Dutch as a note of the Institute (Nota 59, 1978).     

施肥对土壤理化性状及玉米产量的影响

通过10年研究化肥与根茬、秸秆和有机肥定量配比施肥对土壤肥力、养分平衡及玉米产量的影响,结果表明:玉米单施化肥产量下降了7.9%;化肥 根茬产量持平;化肥 根茬 秸秆,土壤肥力和玉米产量同步上升,玉米增产17.1%;化肥 根茬 有机肥效果更佳,土壤肥力指标均上升,玉米增产32.1%。这对制定科学合理的培肥地力施肥措施,建立高产、优质、低耗的培肥制度,具有十分重要的意义。     

Organic matter turnover and management in low input agriculture of NE Brazil

The storage and release of nutrients by soil organic matter (SOM) is the primary determinant of soil fertility in low-input agriculture of semiarid NE Brazil. Traditional shifting cultivation systems have utilised the SOM built up during the fallow phase to supply nutrients for a cultivation phase of some 4–6 years. In this paper we analyse the turnover, stabilisation and quality of organic matter in landuse systems of NE Brazil. This analysis relies on a review of our own and literature data as well as farmers' perceptions recorded in a survey of 240 farms. Components critical for the understanding of SOM balances and transformations are residue inputs under native and agricultural vegetation, rates and controls of SOM mineralisation under cultivation, controls on SOM accretion under fallow vegetation, and the quality of SOM with respect to nutrient supply. While all these factors are known in outline, the detail of understanding that would be required for fine tuning management systems to be sustainable under present (and increasing) production pressure is still lacking. In particular quantity and quality of organic matter inputs from different vegetation types, controls on SOM stabilisation under different cultivation regimes, and the rates and synchrony with plant demand of nutrient release from mineralising organic matter need to be investigated in further detail. This revised version was published online in June 2006 with corrections to the Cover Date.     

腐植酸与硅肥配施对土壤养分的影响

通过盆栽实验,研究腐植酸与硅肥配施对土壤养分的影响。结果表明,施肥量高的处理,提高了土壤养分中的有效硅、水溶性钙、速效钾、有机质含量,碱解氮、速效磷的含量,各种养分含量随着施肥量增加而提高;腐植酸可增加硅肥的有效性。腐植酸与硅肥施肥量均达0.8g/kg时,土壤中各种有效养分含量最高。腐植酸与硅肥配施较二者单独施用时效果好。     

Effects of liming,K fertilization and leaching on K retention,nutrient uptake and dry matter production of maize grown on a Samoan Oxic Inceptisol

Effects of coralline lime and leaching on dry matter production and nutrient uptake by maize (Zea mays) were studied in 21 cm deep leaching columns/pots filled with an Oxic Inceptisol (12 kg) from Alafua, Western Samoa. Ground (<0.25mm) coralline material containing approximately 80% CaCO₃ was used as lime. There were 12 treatments, factorially arranged: 4 liming rates (0, 10.5, 21.0 and 31.5 g pot^–1) which were applied to the top 5 cm of the pots, and 3 K applications (0, 0.69 1.38 g pot^–1) which were applied after the initial leaching period of 10 days (3 1 pot^–1 day^–1) following the lime applications. Leaching continued for 15 more days, using 1 1 pot^–1 day^–1, after K fertilizations. During the initial leaching period, liming intensified K losses. The applied Ca-ions displaced the exchangeable K which was subsequently leached out of the pots. During the second leaching period, liming increased K retention only when K concentrations in the soil were high (treatment receiving 1.38 g K pot^–1). These effects of liming and leaching on K retention were not detectable in the nutrient uptake of maize grown for 50 days after the second leaching period. This may have been because the leaching losses made up only approximately 2 % of the K-turnover in the pots. A calculated nutrient balance for the pots showed that a large portion of K taken up by maize came out of a pool of nonexchangeable K. The Alafua soil had 0.45 % (11.5 cmol(+)kg^–1) total-K, indicating a relatively large K reserve. Since mineralogical studies failed to detect the presence of any known 2:1 minerals, the K reserve of the Alafua soil might be located in amorphous material.The project that made this research possible was supported under Grant No. 936-5542-G-SS-9092 of the Program in Science and Technology Cooperation, AID/ST/AGR, U.S. Agency for International Development     

Farmer adoption of improved nitrogen management technologies in rice farming: technical constraints and opportunities for improvement

Generally, agricultural research is conducted under the controlled conditions of research stations which, in many cases, do not represent farmers'circumstances. Thus, several technologies do not perform well in farmers' fields and so are not adopted by farmers. Many technical factors and management practices constrain the adoption of improved technologies including efficient N management techniques: (a) poor water control; (b) low plant population; (c) partial nutrient application; (d) insufficient weed control; (e) untimely sowing, transplanting, weeding, and/or harvesting; and (f) poor postharvest processing. Unless farmers improve many, if not all, of these conditions, they cannot reap the full benefits of modern rice varieties and related production technologies. In addition, soil-related constraints such as high spatial and temporal variability in nutrient status, nutrient imbalance, poor drainage, soil degradation (salinity, alkalinity, acidity), and subsoil compaction lessen the effectiveness of nutrient management techniques. Similarly, climatic factors such as variable and unpredictable rainfall, drought, flood, low radiation, and extremes in temperature affect crop growth and nutrient use in rice systems. Most of these factors are beyond farmers' control. Stress-tolerant rice varieties and improved management practices are being developed and evaluated on rice farms to tackle soil and climatic constraints, especially in rainfed lowland rice systems. Two of the management strategies rely on better N placement techniques and use of controlled-release fertilizers to improve nutrient use efficiency in rainfed lowlands. Some tools for site-specific N management in rice include chlorophyll meter and leaf color chart which are being evaluated on farmers' fields. Another strategy is the integrated nutrient management to enhance crop nutrition and minimize fertilizer costs. Adequate farmer training is needed to receive, process, and effectively exploit improved rice varieties and related information, knowledge, and technologies.